Color tables (so called test charts) are printed out for the characterization, ink limitation, linearization and profiling of ink jet color printers, and thereafter measured with a manual or automatic color measurement device. Spectral photometers with 45°/0° geometry are thereby used as color measuring devices and the data used are typically L*a*b* or a spectral remissions in the range of 380 nm to 730 nm. Suitable color measurement devices are, for example, the apparatus “Spectrolino” and “i1” of the company Gretag-Macbeth AG, Regensdorf, Switzerland.
Ink limitation and linearization are typically included in the software of the printer, whereby certain printers, for example of the companies Hewlett Packard and Xerox, already include built-in sensors with densitometer functions for the automatic linearization.
ICC profiles are created as known by way of a color management software (for example “Profile Maker” of the company Logo GmbH) on the basis of the measurement data of the color tables.
Ink limitation, linearization and profiling are dependent on different influence factors, for example the condition of the print head, paper type and paper batch, ink type and ink batch, print modus, printer registration, ambient conditions such as temperature and humidity. Preset parameters are generally used for the ink limitation and linearization. The deviations from the nominal value which result from the spread of media batches and the ambient conditions are compensated by the profile. Generic and preset profiles for all possible combinations of media and print modi are however not or at least not always sufficient, which is why in practice upon higher quality demands manually additional local profiles are generated and used.
In order to simplify these actions, it would be desirable to provide a color printer with a built-in measurement device so that the complete characterization (ink limitation, linearization, profiling) for all media (inks, paper) can occur without additional auxiliary devices and manual measurement processes.
A measurement device suitable for this use must fulfill very high demands. Apart from the usual demands with respect to standardized measurement geometry, spectral range, exactness and Constance (repeatability of the measurement results) it must be able to deliver spectral data, colorimetric data and standardized or specific color density data. These requirements can be definitely fulfilled with the currently commercially available spectral photometers, for example the above-mentioned devices “Spectrolino” and “i1” of the company Gretag-Macbeth AG. However, additional limitations still exist with a built-in device with respect to the installation mass (compact shape) and possibly the weight. Furthermore, increased demands exist regarding ambient conditions (temperature, humidity) and the danger of soiling in the vicinity of the printing works (dust, color mist, etc.). Furthermore, the measurement cannot occur in direct physical contact with the medium, since, for example, in ink jet printers the print is humid and mechanically sensitive for a certain amount of time. A built-in device must also be insensitive to mechanical vibrations and have long-lived light sources. Since the spacing from the measured object is subject to variations because of the non-permissible direct physical contact with the measurement device, the measurement device must also be able to handle that. Finally, service friendliness and commercial criteria also play an essential role, since such measurement devices are required in large quantities and therefore able to be economically manufactured. It is therefore especially required that the assembly can be done at the lowest installation and adjustment cost.